1. Field of the Invention
This invention relates to a device for automatically feeding documents to an image processing device such as a copying machine, and more particularly to an automatic document feeding device capable of rationally feeding documents one by one to a document reading portion of the image processing device with efficiency.
2. Description of the Prior Art
An automatic document feeder has been applied widely to a variety of image processing devices such as a copying machine, image reader and facsimile. In the automatic document feeder, the documents stacked on a document supply tray are automatically fed one by one to a document reading portion of the image processing device and extracted from the document reading portion upon completion of a desired processing operation. For example, the copying machine is commonly provided on its top with a transparent platen defining the document reading portion on which the document to be optically read is placed. The document feeder is generally hinged on the top of the copying machine so that it can open upward to manually place the document on the platen.
In general, the document feeding device of this type has a document feeding passage extending from the document supply tray to the document reading portion defined on the platen, along which a plurality of rollers including at least one document draw-out roller (kick roller) for sending out the documents on the document supply tray one by one into the document feeding passage, and at least one pair of register rollers for preventing skew of the document forwarding along the passage are arranged.
As illustrated in FIG. 1A by way of example, a conventional document feeder 1 applied to a stationary copying machine M having a transparent platen P defining a document reading portion R. This document feeder 1 comprises a document supply tray 2 on which one or more documents D are stacked, a document draw-out roller 3 disposed on the bottom of the document supply tray 2 for sending out the documents on the document supply tray 2 one by one, a document feed roller 5 around which a document feeding passage 4 extending from the document supply tray 2 to the document reading portion R is formed, one or more transport rollers 6 arranged in the document feeding passage 4, and paired registering rollers 7 being in contact with each other for correcting skew of the document forwarding aslant along the document feeding passage 4. This document feeder 1 is found in, for instance, Japanese Utility Model Application Public Disclosure No. SHO 63-35740(A).
When giving an image-processing instruction to the copying machine M, the lowermost one of the stacked documents D on the document tray 2 is sent into the document feeding passage 4 by rotating the draw-out roller 3 and forwarded by the rotating feed roller 5 and transport roller 6 until it collides with the registering rollers 7. Immediately after the document collides with the registering rollers 7, the registering rollers 7 so far stopped starts to rotate to advance the document toward the document reading portion R.
In some cases, the draw-out roller, feed roller 5 and registering rollers 7 in the document feeder are driven by independent driving means including electric motors 8 because these rotating elements should be driven with exquisite timing. Such a document feeder adopting a plurality of driving means enjoys an advantage in that the rotation transmission mechanism of its driving system can be made relatively simple but has the disadvantage that it adds to the size and weight.
In general, the document feeder has a driving and rotation transmitting system 9 including belts or gears as illustrated in FIG. 1B. However, this document feeder with such a driving and rotation transmitting system drives the rollers to rotate all at once during transporting the document, resulting in reduction of efficiency and occurrence of harsh noises. In the document feeder mentioned in Japanese Patent Publication No. SHO 62-5858(B) (corresp. to Japanese Patent Disclosure No. SHO 58-31837(A)), the feed roller 5 driven through an electromagnetic clutch 5a so as to be rotated only when the document comes into contact with the feed roller while advancing along the document feeding passage. Of course, the rotating transmission means for driving the registering rollers 7 incorporates an electromagnetic clutch 7a to temporarily stop the registering rollers 7.
In any case, during the forwarding of the document around the feed roller 5, one or more of the draw-out roller 3, transport roller 6 and registering rollers 7, which do not directly help the document to advance at that time, are rotated together with the rotating feed roller 5. Each roller is generally composed of a plurality of roller elements of the number in conformity with the width of the document reading portion of the image processing device. Therefore, it requires relatively large kinetic energy to rotate the respective rollers, resulting in generation of harsh noises during rotation. Thus, it is desirable to interrupt the rotation of the rollers which rotates, but do not exert the forward movement to the document.
However, this conventional document feeder having the electromagnetic clutchs, as illustrated in FIG. 1B, for temporarily stopping the rollers which do not serve to forward the document has a disadvantage of making the rotation transmitting mechanism and control system complicated and large in size and turning out to be expensive and susceptible to mechanical troubles during service.